Radiation curable powder coating compositions

ABSTRACT

A radiation curable powder coating composition is disclosed, which comprises a blend of (meth)acryloyl group containing polyphenoxy resin, a (meth)acryloyl group containing resin other than the polyphenoxy resin and other than a (meth)acryloyl group containing amorphous polyester and, eventually, a (meth)acryloyl group containing monomer or oligomer. These powders give coatings with improved chemical resistance and flexibility.

The present invention concerns powder compositions, hardenable byradiation usable as paint or varnish, comprising a mixture of at leastone (meth)acryloyl group containing polyphenoxy resin and at least one(meth)acryloyl group containing resin different from the polyphenoxyresin and from a (meth)acryloyl group containing amorphous polyester,and optionally at least one (meth)acryloyl group containing monomer oroligomer.

The powder compositions of the present invention are especially suitedfor coating over metal and heat-sensitive substrates and combine, uponmelting at low temperatures and curing by radiation, a series ofproperties such as good flow along with an outstanding solventresistance and flexibility.

Powder coatings, which are dry, finely divided, free flowing, solidmaterials at room temperature, have gained considerable popularity inrecent years over liquid coatings. Despite their many advantages,nowadays thermosetting powder coatings generally are cured attemperatures of at least 140° C. Below this recommended temperature thecoatings have poor appearance as well as poor physical and chemicalproperties. In consequence of this restriction, powder coatings aregenerally not employed in coating heat-sensitive substrates such as woodand plastic or assembled metallic parts containing heat-sensitivecompounds. Heat-sensitive substrates or compounds both demand low curingtemperatures, preferably below 140° C., to avoid significant degradationand/or deformation.

Low temperature radiation curable powders have recently been proposed asa solution to this problem.

The use of unsaturated resins, eventually in combination withunsaturated oligomers, as a binder for radiation curable powder coatingsalready is subject of a considerable number of patents and patentapplications.

UV curable powder coating compositions derived from ethylenicallyunsaturated group containing polyesters, acrylic copolymers or epoxyresins, among others, already have been extensively illustrated.

U.S. Pat. No. 3,974,303 (Kansai Paint Co Ltd.) describes differentunsaturated resins such as methacryloyl group containing polyesters oracrylic copolymers.

DE 2164254 (BASF) describes powder coatings based on unsaturatedpolyesters, acrylic copolymers, epoxy resins and other polymerscontaining unsaturated double bonds.

U.S. Pat. No. 4,129,488 (SCM Corporation N.Y.) discloses powder paintcoatings suitable for UV curing comprising a specific spatialarrangement of ethylenically unsaturated polymers. The (meth)acrylicunsaturated polymer is a spatial specific epoxy-polyester polymer,produced in a step-wise process, with a number average molecular weightbetween 1000 and 10 000, providing suitable crystallinity to the freeflowing powder and exhibiting a sharp melting point, between 80 and 200°C., for excellent flow.

The powder paints derived from the spatial specific epoxy polyesterpolymer prove excellent hardness, desirable flexibility and good MEKresistance.

Radiation curable powder coatings, especially developed for thoseapplications where an outstanding flexibility and chemical resistance isneeded, all fall short when outdoor durability is concerned.

It now has been surprisingly found that radiation curable powder coatingcompositions based on a binder comprising a particular mixture of atleast one (meth)acryloyl group containing polyphenoxy resin, at least(meth)acryloyl group containing resin, different from the polyphenoxyresin and from a (meth)acryloyl group containing amorphous polyester,and optionally at least one (meth)acryloyl group containing monomer oroligomer, upon application and curing exhibit an excellent combinationof flexibility and solvent resistance.

It is accordingly the object of this invention to provide a radiationcurable powder coating composition which comprises:

-   -   a) 10 to 90% weight of at least one (meth)acryloyl group        containing polyphenoxy resin    -   b) 10 to 90% weight of at least one (meth)acryloyl group        containing resin, different from the (meth)acryloyl group        containing polyphenoxy resin a) and from a (meth)acryloyl group        containing amorphous polyester    -   c) 0 to 30% weight of a (meth)acryloyl group containing monomer        or oligomer.

The (meth)acryloyl group containing resin b) is selected fromsemi-crystalline polyester, polyesteramide, polyurethane or polyacryliccopolymer, used alone or in admixture.

The (meth)acryloyl group containing polyphenoxy resin is prepared fromthe reaction of the glycidyl group of the polyphenoxy resin with:

-   -   (meth)acrylic acid    -   the reaction product of an hydroxyalkylester of (meth)acrylic        acid such as hydroxyethyl(meth)acrylate with an anhydride such        as phthalic anhydride or succinic anhydride.

For the preparation of the (meth)acryloyl group containing polyphenoxyresin, use is generally made of a conventional reactor equipped with astirrer, an inlet for oxygen, an inlet for the (meth)acryloyl groupcontaining carboxylic acid group containing compound and a thermometerconnected to a thermoregulator. To the epoxy resin standing at atemperature between 100 and 150° C., a radical polymerisation inhibitoris added in a proportion of e.g. 0.01 to 1% with respect to the weightof the epoxy resin. A substantial equivalent amount of the(meth)acryloyl group containing carboxylic acid group containingcompound is then slowly added to the molten epoxy resin. A catalyst forthe acid/epoxy reaction can optionally be used. Examples of suchcatalysts include amines (e.g. 2-phenylimidazoline), phosphines (e.g.triphenylphosphine), ammonium salts (e.g. tetrabutylammonium bromide ortetrapropylammonium chloride), phosphonium salts (e.g.ethyltriphenylphosphonium bromide or tetrapropylphosphonium chloride).These catalysts are preferably used in an amount of 0.05 to 1% withrespect to the weight of the epoxy resin.

The degree of progression of the reaction is monitored by determinationof the properties of the ethylenically unsaturated group containingresin obtained, such as acid number, hydroxyl number and the degree ofunsaturation.

The (meth)acryloyl group containing polyphenoxy resins incorporated inthe compositions in accordance with the present invention, preferablyexhibit a degree of unsaturation of 0.2 to 6.0, particularly of 0.5 to4.5 milliequivalents of double bonds per gram of resin, and in aspecifically preferred embodiment additionally exhibit the followingcharacteristics:

-   -   a number average molecular weight (Mn) from 450 to 5000,        preferably between 650 and 3500, measured by gel permeation        chromatography (GPC)    -   a glass transition temperature (Tg) determined by differential        scanning calorimetry (DSC) according to ASTM D3418, from 30 to        80° C.    -   a viscosity in the molten state measured at 200° C. with a        cone/plate viscometer (known under the name of ICI viscosity)        according to ASTM D4287, of less than 20 000 mPa.s.

The (meth)acryloyl group containing polyesters of the present inventionare semi-crystalline and are prepared from the reaction of a hydroxyl orcarboxylic acid functional semi-crystalline polyester with a(meth)acryloyl group containing monomer having functional groupsreactable with the functional groups of the polyester.

For the preparation of the hydroxyl or carboxylic acid functionalsemi-crystalline polyester use is being made of one or more aliphatic,cycloaliphatic or aromatic polyacids and one or more aliphatic orcycloaliphatic polyols. Examples of suitable aliphatic, cycloaliphaticor aromatic acids include among others: phthalic acid, isophthalic acid,terephthalic acid, 1,2-cyclohexanedicarboxylic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid,azelaic acid, sebacic acid, 1,12-dodecanedioic acid, trimellitic acid,pyromellitic acid and their anhydrides, alone or as a mixture.

Examples of suitable aliphatic or cycloaliphatic polyols include amongothers: ethylene glycol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol,2-methyl-1,3-propanediol, neopentyl glycol,2-butyl-2-methyl-1,3-propanediol, hydroxypivalate ester of neopentylglycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenatedBisphenol A, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,4,8-bis(hydroxymethyl)-tricyclo-[5,2,1,0^(2,6)]-decane.

The hydroxyl or carboxylic acid group containing semi-crystallinepolyesters of the present invention are prepared according a procedurecomprising one or more reaction steps.

On completion of the polycondensation, the hydroxyl or carboxylfunctional group containing semi-crystalline polyester in the moltenstate, which is found in the reactor, is allowed to cool to atemperature between 100 and 160° C., and a radical polymerisationinhibitor, such as phenothiazine or an inhibitor of the hydroquinonetype, is added in a proportion of e.g. 0.01 to 1% with respect to theweight of the polyester and the nitrogen is replaced by an oxygen inlet.

When started from a hydroxyl group containing semi-crystallinepolyester, a substantially equivalent amount ofhydroxyalkyl(meth)acrylate is added thereto. When all thehydroxyalkyl(meth)acrylate is added, an equivalent amount ofdiisocyanate is slowly added to the mixture. A catalyst for thehydroxyl/isocyanate reaction can optionally be used. Examples of suchcatalysts include organo-tin compounds (e.g. dibutyltin dilaurate,dibutyltin dimaleate, dibutyltin oxide, stannous octoate,1,3-diacetoxy-1,1,3,3-tetrabutyl-distanoxane). These catalysts arepreferably used in an amount of 0 to 1% with respect to the weight ofthe polyester.

Otherwise, when started from a semi-crystalline polyester containingcarboxyl groups, a substantially equivalent amount ofglycidyl(meth)acrylate is added thereto. A catalyst for the acid/epoxyreaction can optionally be used. Examples of such catalysts includeamines (e.g. 2-phenylimidazoline), phosphines (e.g. triphenylphosphine),ammonium salts (e.g. tetrabutylammonium bromide or tetrapropylammoniumchloride), phosphonium salts (e.g. ethyltriphenylphosphonium bromide ortetrapropylphosphonium chloride). These catalysts are preferably used inan amount of 0.05 to 1% with respect to the weight of the polyester.

The degree of progression of the reaction is monitored by determinationof the properties of the semi-crystalline polyester obtained, forexample the hydroxyl number, the acid number, the degree of unsaturationand/or the content of free glycidyl(meth)acrylate orhydoxyalkyl(meth)acrylate.

The (meth)acryloyl group containing semi-crystalline polyesters of thepresent invention are characterised with a number average molecularweight (Mn) from 800 to 16 000 and preferably from 1 300 to 8 500, amelting temperature from 60 to 150° C. and a glass transitiontemperature of less than 50° C., a degree of unsaturation ranging from0.15 to 2.00 and preferably from 0.35 to 1.50 milliequivalents of doublebonds per gram of polyester and an ICI cone/plate viscosity of less than50 000 mPa.s measured at 200° C.

The (meth)acryloyl group containing polyesteramides of the presentinvention are prepared from the reaction of glycidyl(meth)acrylate witha carboxyl group terminated polyesteramide, said polyesteramide beingprepared from the reaction of a carboxyl group terminated polyester witha diamine.

The carboxyl group terminated polyesters used for the synthesis of thepolyesteramides are prepared from aliphatic, cycloaliphatic or aromaticpolyacids used in a mixture or alone, and aliphatic or cycloaliphaticpolyols used in a mixture or alone, both, the polyacids and the polyolsbeing selected among these examples as recited earlier for thepreparation of the (meth)acryloyl group containing semi-crystallinepolyesters.

Examples of the diamines which can be used, either alone or incombination, for the preparation of the polyesteramides are selectedfrom ethylenediamine, 1,3-propanediamine, 1,5-pentanediamine,1,6-hexanediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine,1,4-cyclohexanediamine, 2,2-dimethyl-1,3-propanediamine,N-(2-iaminoethyl)-1,2-ethanediamine,3,3′-dimethyl-4,4′-diaminodicyclohexylmethane,4,4′-diaminodicyclohexylmethane,3,3′-dimethyl-4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethaneand analogous compounds.

The polyesteramides used for the preparation of the (meth)acryloyl groupcontaining polyesteramides are prepared accordingly a two or more stepprocedure process as disclosed in U.S. Pat. No. 5,306,786.

On completion of the synthesis of the carboxylic acid group containingpolyesteramide, a substantially equivalent amount ofglycidyl(meth)acrylate is added thereto, accordingly a procedure asdescribed above for the preparation of the (meth)acryloyl groupcontaining semi-crystalline polyesters starting from the carboxylic acidgroup functional polyester, to end up with a (meth)acryloyl groupcontaining polyesteramide characterised by a number average molecularweight (Mn) from 800 to 16 000 and preferably from 1 300 to 8 500, aglass transition temperature (Tg) from 40 to 70° C., a degree ofunsaturation ranging from 0.15 to 2.00 and preferably from 0.35 to 1.50milliequivalents of double bonds per gram of polyesteramide and an ICIcone/plate viscosity of less than 50 000 mPa.s measured at 200° C.

The (meth)acryloyl group containing polyurethanes of the presentinvention are prepared from the reaction of anhydroxyalkyl(meth)acrylate and a polyol with a polyisocyanate.

The polyol used for the preparation of the (meth)acryloyl groupcontaining polyurethanes are chosen among the C2–C15 aliphatic orcycloaliphatic diols, polyester polyols or polyether polyols.

Examples of C2–C15 aliphatic or cycloaliphatic diols are ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol,2-methyl-1,3-propanediol, neopentyl glycol,2-butyl-2-methyl-1,3-propanediol, hydroxypivalate ester of neopentylglycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenatedBisphenol A, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,4,8-bis(hydroxymethyl)-tricyclo-[5,2,1,0^(2,6)]-decane.

The polyester polyols, characterised by number average molecular weight(Mn) from 8200 to 4000, are prepared from a stoichiometric excess of analiphatic or cycloaliphatic polyol with an aromatic, aliphatic orcycloaliphatic polyacid, the polyacids and the polyols being selectedamong those recited earlier for the preparation of the (meth)acryloylgroup containing semi-crystalline polyesters or polyesteramides.

Examples of the polyether polyols are polyoxyethylene glycol,polyoxypropylene glycol, polyoxybutylene glycol, polytetramethyleneglycol, block copolymers, for example, combinations of polyoxypropyleneand polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethyleneglycols, poly-1,4-tetramethylene and polyoxyethylene glycols, andcopolymer glycols prepared from blends or sequential addition of two ormore alkylene oxides. The polyalkylene polyether polyols may be preparedby any known process such as, for example, the process disclosed inEncyclopaedia Technology, Vol. 7, pp. 257–262, published by IntersciencePublishers, Inc. (1951).

Examples of polyisocyanates that can be used for the preparation of the(meth)acryloyl group containing polyurethanes of the present inventionare 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane(isophorondiisocyanate, IPDI), tetramethylxylenediisocyanate (TMXDI),hexamethylenediisocyanate (HDI), trimethylhexamethylenediisocyanate,4,4′-diisocyanatodicyclohexylmethane, 4,4′-diisocyanatodiphenylmethane,these technical mixtures with 2,4-di-isocyanatodiphenylmethane and alsothe higher homologues of above mentioned diisocyanates,2,4-di-isocyanatotoluene and technical mixtures of them with2,6-diisocyanatotoluene, as well as the copolymerisation product ofα,α′-dimethyl-meta-isopropenylbenzylisocyanate (TMI).

The hydroxyalkyl(meth)acrylate used for the preparation of the(meth)acryloyl group containing polyurethanes are hydroxyalkylesters ofacrylic or methacrylic acid preferably having 2 to 4 carbon atoms in thehydroxyalkyl group such as hydroxyethyl(meth)acrylate, 2- and3-hydroxypropyl(meth)acrylate and 2-, 3- and4-hydroxybutyl(meth)acrylate.

Preparation of the polyurethanes by reacting the above mentionedstarting components may be carried out in inert solvents such asacetone, ethyl acetate, butyl acetate or toluene, preferably at reactiontemperatures of 20 to 100° C. The reaction is preferably carried out byreacting the polyisocyanate with the hydroxyalkyl(meth)acrylate in afirst reaction step and then reacting the resulting reaction productwith the polyol.

The reaction may be accelerated by the use of suitable catalysts such astin octoate, dibutyltin dilaurate or tertiary amines such asdimethylbenzylamine. The polyurethane or urethane acrylate obtained asthe reaction product may be protected against premature, unwantedpolymerisation by the addition of suitable inhibitors and antioxidantssuch as phenols and/or hydroquinones in quantities of 0.001 to 0.300% byweight, based on the polyurethane. These auxiliary agents may be addedbefore, during and/or after the reaction which results in thepolyurethane.

The (meth)acryloyl group containing polyurethanes of the presentinvention are characterised by a number average molecular weight (Mn)from 800 to 15 000 and preferably from 1 300 to 8 500, a glasstransition temperature (Tg) from 40 to 100° C., a degree of unsaturationranging from 0.15 to 0.20 and preferably from 0.35 to 1.50milliequivalents of double bonds per gram of polyurethane and an ICIcone/plate viscosity of less than 100 000 mPa.s measured at 200° C.

The (meth)acryloyl group containing acrylic copolymers of the powdercomposition of the present invention are prepared from the reaction of(meth)acryloyl group containing monomers having functional groups withan acrylic copolymer having functional groups being capable of reactingwith the functional groups of the (meth)acryloyl group containingmonomers.

The acrylic copolymer having reactable functional groups is composed offrom 40 to 95% mole of at least one acrylic or methacrylic monomer, from0 to 60% mole of at least one other ethylenically unsaturated monomerand from 5 to 60% mole of a (meth)acryloyl group containing monomerhaving functional groups selected from epoxy, carboxyl, hydroxyl orisocyanate groups.

The (meth)acryloyl group containing acrylic copolymer of the powdercomposition of the present invention is prepared accordingly a two stepprocess.

In a first step the acrylate copolymer is prepared in a conventionalpolymerisation process, such as polymerisation in bulk, in emulsion, orin solution in an organic solvent, in which a certain portion offunctional monomer is copolymerised to obtain a functionalised acrylatecopolymer. This functional monomer, which is usually present in amountsof between 5 and 60% mole, is preferably an epoxy—functional monomer,for example on the basis of glycidyl (meth)acrylate. However,acid-functional monomers, for example on the basis of (meth)acrylicacid, hydroxyl-functional monomers, for example on the basis ofhydroxyethyl (meth)acrylate, or isocyanate-functional monomers, forexample on the basis of TMI (benzene,1-(1-isocyanato-1-methylethyl)-4-(1-methylethenyl)) or MOI(2-isocyanatoethylmethacrylate) also can be used.

The monomers are copolymerised in the presence of free-radical initiatorsuch as benzoyl peroxide, tert.-butyl peroxide, decanoyl peroxide,azo-bis-isobutyronitrile, and the like, in an amount of from 0.1 to 5%by weight of the monomers. Useful monomers for the preparation of theacrylic copolymer are methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate,tert.-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,stearyl(meth)acrylate, tridecyl(meth)acrylate, cyclohexyl(meth)acrylate,benzyl(meth)acrylate, phenyl(meth)acrylate,dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate,polysiloxane (meth)acrylate and caprolactone(meth)acrylate. Thesemonomers usually are present in amounts between 40 and 95% mole.

Other copolymerisable monomers, which can be present in amounts between0 and 60% mole, are for example styrene, α-methylstyrene, vinyltoluene,acrylonitrile, methacrylonitril, vinyl acetate, vinyl propionate,acrylamide, methacrylamide, methylolmethacrylamide, vinylchloride,ethylene, propylene and C4–20 α-olefins.

In the second step an addition reaction is carried out between thefunctionalised monomer of the acrylate copolymer obtained from the firststep and the (meth)acryloyl group containing compound that can reactwith said functional monomer. The compound that can react respectivelyis for example (meth)acrylic acid, maleic anhydride,(β-methyl)glycidyl(meth)acrylate, allylglycidylether, MOI, hydroxyethyl(meth)acrylate, hydroxybutylvinylether, allylalcohol.

The addition reaction of the second step can be done either in bulk orin solvent. Typical solvents are toluene, xylene, n-butylacetate, etc.The compound containing an (meth)acryloyl group that can react with thefunctionalised acrylate polymer is added at temperatures between 50 and150° C. The mixture is stirred for several hours. The progress of thereaction is followed by titration.

The (meth)acryloyl group containing acrylic copolymer of the powdercomposition of the present invention exhibit following characteristics:

-   -   a number average molecular weight (Mn) from 1000 to 8000 and        preferably from 2 000 to 6 000 measured by GPC    -   a degree of unsaturation from 0.35 to 3.50 and preferably from        0.5 to 2.5 milliequivalents of double bounds per gram of acrylic        copolymer    -   an ICI cone/plate melt viscosity of less than 50 000 mPa.s        measured at 200° C. according to ASTM D4287    -   a glass transition temperature (Tg) from 45 to 100° C. as        determined by DSC according to ASTM D3418

Besides, up to 30% weight of the composition of the invention may beconstituted of a (meth)acryloyl group containing monomer or oligomerselected from the triacrylate and the tri(meth)acrylate oftris(2-hydroxyethyl)isocyanurate, the epoxy acrylates and methacrylateswhich are formed by the reaction of an epoxy compound (for example, thediglycidyl ether of Bisphenol A) with acrylic or methacrylic acid, theurethane acrylates and methacrylates which are formed by the reaction ofan organic di- or polyisocyanate with an hydroxyalkylacrylate or ahydroxyalkylmethacrylate and optionally a mono- and/or polyhydroxylatedalcohol (for example, the reaction product of hydroxyethyl(meth)acrylatewith toluenediisocyanate or isophoronediisocyanate), the acrylicacrylates or methacrylates, such as, for example, the reaction productof (meth)acrylic acid with a copolymer containing glycidyl groups andmethylmethacrylate, and the like.

The polyphenoxy resin, the semi-crystalline polyester and/or thepolyesteramide and/or polyurethane and/or acrylic copolymer optionallyalong with one or more monomers or oligomers all containing(meth)acryloyl groups all described above, intended to be used asbinders in the preparation of powder compositions curable by UVradiation or by accelerated electron beams, it being possible for thesaid compositions to be used in particular as varnishes and paints whiche.g. lend themselves to application according to the technique ofdeposition by means of a triboelectric or electrostatic spray gun oraccording to the technique of deposition in a fluidised bed. Theradiation curable powder compositions can be used as varnishes or paintsas such or, if desired, the compositions can be used to prepare thevarnishes or paints by adding, further constituents conventionally usedin the preparation of powder varnishes and paints.

Therefore, the present invention also relates to the powder varnish orpaint obtained using these compositions.

Finally, the present invention also relates to a process for coating anarticle more particularly a metal article comprising the application tothe said article of a radiation curable powder composition in accordancewith the invention by deposition such as by spraying with atriboelectric or electrostatic spray gun or by deposition in a fluidisedbed, followed by the melting of the coating thus obtained such as byheating at a temperature of 80 to 150° C. for a time of e.g.approximately 0.5 to 10 minutes and by the curing of the coating in themolten state by UV irradiation or by accelerated electron beams.

For the radiation curing of the powder compositions in accordance withthe invention with accelerated electron beams, it is not necessary touse a photo-initiator, seeing that this type of radiation provides byitself alone a production of free radicals which is sufficiently highfor the curing to be extremely rapid. In contrast, when it concerns thephoto-curing of the powder composition according to the invention withradiation where the wavelengths are between 200 and 600 nm (UVradiation), the presence of at least one photo-initiator is essential.

The photo-initiators which can be used according to the presentinvention are chosen from those commonly used for this purpose.

The appropriate photo-initiators which can be used, are aromaticcarbonyl compounds, such as benzophenone and its alkylated orhalogenated derivatives, anthraquinone and its derivatives, thioxanthoneand its derivatives, benzoin ethers, aromatic or non-aromaticalphadiones, benzil dialkyl acetals, acetophenone derivatives andphosphine oxides.

Photo-initiators which may suitable, are, for example,2,2′-diethoxylacetophenone, 2-,3- or 4-bromoacetophenone,2,3-pentanedione, hydroxycyclohexylphenylketone, benzaldehyde, benzoin,benzophenone, 9,10-dibromoanthracene,2-hydroxy-2-methyl-1-phenylpropan-1-one, 4,4′-dichlorobenzophenone,xanthone, thioxanthone, benzildimethylketal,diphenyl(2,4,6-trimethylbenzyl)phosphine oxide, and the like. It may beoptionally advantageous to use a photo-activator, such as tributylamine,2-(2-aminoethylamino)ethanol, cyclohexylanine, diphenylamine,tribenzylamine or aminoacrylates such as, for example, the additionproduct of a secondary amine, such as dimethylamine, diethylamine,diethanolamine, and the like, with a polyol polyacrylate, such as thediacrylate of trimethylolpropane, 1,6-hexanediol, and the like. Thepowder compositions in accordance with the invention can contain 0 to 15and preferably 0.5 to 8.0 parts of photo-initiators for 100 parts byweight of the binder in the composition in accordance with theinvention.

The radiation curable powder compositions and powder varnishes orpaints, respectively, in accordance with the invention can also containvarious additional substances conventionally used in the manufacture ofpowder paints and varnishes. The additional substances optionally addedto the radiation-curable powder compositions in accordance with theinvention, e.g. to prepare the powder varnishes or paints are, interalia, compounds which absorb UV radiation, such as Tinuvin 900 (Ciba),light stabilisers based on sterically hindered amines (for exampleTinuvin 144 from Ciba), fluidity-regulating agents such as Resiflow PV5(Worlee), Modaflow (Monsanto), Acronal 4F (BASF) or Crylcoat 109 (UCB),degassing agents such as benzoin and the like.

To the radiation-curable powder composition according to the presentinvention, further can be added a variety of coating propertiesmodifying substances such as polytetrafluoroethylene modifiedpolyethylene waxes (e.g. Lanco Wax TF 1830 from Lubrizol), polyethylenewaxes (e.g. Ceraflour 961 from BYK Chemie), polypropylene waxes (e.g.Lanco Wax PP1362 from Lubrizol), polyamide waxes (e.g. Orgasol 3202 DNAT from ELF Atochem), organosilicones (e.g. Modarez S304P from Protex),etc., or blends of them. These modifying substances are optionally addedfrom 0 to 10 parts for 100 parts by weight of the binder in thecomposition according to the invention. A variety of pigments andinorganic fillers can also be added to the radiation curable powdercompositions in accordance with the invention. Mention will be made, asexamples of pigments and fillers, of metal oxides, such as titaniumoxide, iron oxide, zinc oxide, and the like, metal hydroxides, metalpowders, sulphides, sulphates, carbonates, silicates such as, forexample, aluminium silicate, carbon black, talc, kaolins, barytes, ironblues, lead blues, organic reds, organic maroons, and the like.

These additional substances are used in the usual amounts, it beingunderstood that if the radiation curable powder compositions inaccordance with the present invention are used as varnishes, theaddition of additional substances having opacifying properties should beomitted.

For the preparation of the radiation curable powder compositions of thepresent invention the polyphenoxy resin, the semi-crystalline polyesterand/or the polyesteramide and/or polyurethane and/or acrylic copolymeroptionally along with one or more monomer or oligomer all containing(meth)acryloyl groups, optionally the photo-initiator, optionally thevarious additional substances conventionally used for the manufacturingof powder paints and varnishes, and optionally the coating propertiesmodifying substances are dry mixed, for example in a tumbler mixer. Themixture is then homogenised at a temperature ranging from 60 to 150° C.in an extruder, for example in a Buss Ko-Kneter single screw extruder ora twin screw extruder of Werner-Pfleiderer, APV-Baker or Prism type. Theextrudate is then allowed to cool, is ground and sieved in order toobtain a powder in which the size of the particles is preferably between10 and 150 μm.

Instead of the above methods, it is also possible to dissolve/suspendthe different unsaturated constituents of the binder system of thepresent invention, optionally the photo-initiator, and the variousadditional substances in a solvent such as dichloromethane, to grind inorder to obtain a homogeneous suspension containing approximately 30% byweight of solid matter and subsequently to evaporate the solvent, forexample by spray drying at a temperature of approximately 50° C.,according to methods known per se.

The powder paints and varnishes thus obtained, are entirely suitable forapplication to the article to be coated by conventional techniques, thatis to say by the well-known technique of e.g. deposition in a fluidisedbed or by application with a triboelectric or electrostatic spray gun.

After having been applied to the article concerned, the coatingsdeposited are heated e.g. in a forced circulation oven or by means ofinfrared lamps at a temperature of 80 to 150° C. for a time of e.g.approximately 0.5 to 10 minutes for the purpose of obtaining the meltingand the spreading of the powder particles as a smooth, uniform andcontinuous coating at the surface of the said article. The moltencoating is then cured by radiation, such as UV light emitted, forexample, by medium pressure mercury vapour UV radiators, of preferablyat least 80 to 250 W/linear cm, or by any other well-known source of thestate of the art, at a distance of e.g. approximately 5 to 20 cm and fora time sufficient to cure the coating, such as 1 to 60 seconds.

The molten coating can also be cured with accelerated electron beams ofpreferably at least 150 keV, the power of the devices employed being adirect function of the thickness of the composition layer to be cured bypolymerisation.

The invention is also concerned by articles partially or entirely coatedby the coating processes.

The radiation curable powder compositions in accordance with theinvention can be applied to the most diverse substrates, such as, forexample, metal, paper, cardboard, wood, fibre board, textiles, plastics,such as polycarbonates, poly(meth)acrylates, polyolefins, polystyrenes,poly(vinylchloride)s, polyesters, polyurethanes, polyamides, copolymerssuch as acrylonitrile-butadiene-styrene (ABS) or cellulose acetatebutyrate, and the like.

The radiation curable powder compositions in accordance with theinvention can also be formulated in toner compositions.

The examples which follow, illustrate the invention without limiting it.Except when otherwise indicated, the parts mentioned throughout thedescription and in the examples are parts by weight.

EXAMPLE 1

Synthesis of a Semi-Crystalline Polyester Containing End MethacryloylGroups in Three Steps

1st Step

258.4 parts of 1,6-hexanediol, 10.4 parts of trimethylolpropane and 1.9parts of n-butyltin trioctoate, as catalyst, are introduced into afour-necked round-bottomed flask equipped with a stirrer, a distillationcolumn connected to a water-cooled condenser, a nitrogen inlet pipe anda thermometer connected to a thermoregulator. The mixture is heated in anitrogen atmosphere and with stirring to a temperature of approximately140° C., 484.4 parts of terephthalic acid are then added, still withstirring, and the mixture is heated to a temperature of 190° C., atwhich the water formed begins to distil. The heating in then continuedgradually until the mass reaches a temperature of 230° C. Afterapproximately 95% of the theoretical amount of water formed has beencollected, a transparent polyester is obtained.

The semi-crystalline polyester containing end hydroxyl groups thusobtained exhibits the following characteristics:

-   -   AN=9.5 mg KOH/g    -   OHN=42 mg KOH/g    -   ICI175° C.=700 mPa.s        2nd Step

The polyester containing end hydroxyl groups obtained in the first stepis allowed to cool to 200° C. and 75 parts of isophthalic acid are addedthereto. The reaction mixture is then gradually heated to thetemperature of 230° C. The reaction mixture is left at this temperaturefor approximately two hours, until the reaction mixture becomestransparent, and the pressure is then gradually decreased for threehours at 230° C. under reduced pressure.

The semi-crystalline polyester containing end carboxyl groups thusobtained exhibits the following characteristics:

-   -   AN=31 mg KOH/g    -   OHN=1 mg KOH/g    -   ICI175° C.=7 450 mPa.s    -   Mn (GPC)=4 550        3rd Step

The polyester containing end carboxyl groups obtained in the second stepis allowed to cool to 150° C., and 0.4 part of di-t-butylhydroquinone,as polymerisation inhibitor, and 4.1 parts of ethyltriphenylphosphonium,as catalyst, are added thereto. 62.2 parts of glycidylmethacrylate arethe added thereto slowly in an oxygen atmosphere and with stirring. Onehour after the addition has been completed, a semi-crystalline polyestercontaining end methacryloyl groups is obtained which exhibits thefollowing characteristics:

-   -   AN=1.5 mg KOH/g    -   OHN=32 mg KOH/g    -   unsaturation=0.5 meq/g    -   ICI175° C.=5 300 mPa.s    -   Tm(quenched—DSC, 20°/min)=101° C.    -   Mn (GPC)=4 890

EXAMPLE 2

221.3 parts of n-butylacetate are brought in a double walled flask of 5l equipped with a stirrer, a water cooled condenser an inlet fornitrogen and a thermoprobe is attached to a thermoregulator.

The flask content is heated and stirred continuously while nitrogen ispurged through the solvent. At a temperature of 110° C. a mixture of234.7 parts of n-butylacetate with 13.4 parts of2,2′-azobis(2-methylbutanenitrile) is fed in the flask during 215minutes with a peristaltic pump. Five minutes after the start of thisfeed, a second feed is started with another pump and is a mixture of:

-   -   102.7 parts of hydroxyethylmethacrylate    -   88.5 parts of isobornylacrylate    -   162.9 parts of methylmethacrylate    -   88.5 parts of n-butylmethacrylate

This feed takes 180 minutes.

The acrylic copolymer having hydroxyl functional groups andcharacterised by:

-   -   OHN=96 mg KOH/g    -   ICI125° C.=22 500 mPa.s    -   Tg (quenched—DSC, 20°/min)=53° C.        then is transversed as a solution in a round bottom single        walled flask.

The solution is heated to 40° C. and air is continuously purged through.After 30 minutes 0.09 parts of Norsocryl 200 (inhibitor commercialisedby Elf Atochem) and 87.6 parts of 2-isocyanotoethylmethacrylate areadded in 180 minutes. The isocyanate number is checked regularly throughback-titration of dibutylamine with hydrochloric acid. When theisocyanate content is less than 0.3% of the initial value the flaskcontent is cooled down and dried in a rotary evaporator at 30° C.

The ethylenically unsaturated acrylic copolymer thus prepared ischaracterised by following characteristics:

-   -   unsaturation=1.45 meq/g    -   ICI100° C.=50 000 mPa.s    -   Tg (quenched—DSC, 20′/min)=51° C.    -   Mn (GPC)=3125

EXAMPLE 3

In a conventional four-neck round bottom flask equipped with a stirrer,an inlet for oxygen, an inlet for (meth)acrylic acid and a thermocoupleattached to a thermoregulator, 910 parts of Araldite GT7004, a BisphenolA-type epoxy resin, are heated under oxygen to a temperature of 140° C.Subsequently 0.8 parts of ethyltriphenylphosphonium bromide are addedand the addition of 90 parts of acrylic acid containing 0.2 parts ofdi-t-butylhydroquinone, is started. The acrylic acid addition iscompleted in a 3 hour period. One and an half hour after the completionof the acrylic acid addition, a resin with the following characteristicsis obtained:

-   -   AN=7 mg KOH/g    -   unsaturation=1.24 meq/g    -   ICI200° C.=700 mPa.s    -   Tg (quenched—DSC, 20°/min)=49° C.    -   Mn (GPC)=1650

EXAMPLE 4 AND 5

Two white powders which can be used for the manufacturing of coatings byspraying with the aid of an electrostatic spray gun are prepared fromblends of the methacryloyl group containing resins of example 1 and 2respectively, with the methacryloyl group containing polyphenoxy resinof example 3, the formulation of these powders being as follows:

White powder formulation 750.0 parts binder titanium dioxide (Kronos2310 (Kronos)) 250.0 parts α-hydroxyketone (Irgacure 2959 (Ciba)) 12.5parts bisacylphosphineoxide (Irgacure 819 (Ciba)) 12.5 parts fluidityregulating agent (Resiflow PV5 (Worlee Chemie)) 10.0 parts

These powder compositions are prepared by dry mixing the differentingredients. The mixture obtained is homogenised at a temperature ofapproximately 70 to 140° C. in a Prism 16 mm (L/D=15/1) twin screwextruder (from the company Prism), and the extrudate is ground in agrinder of Alpine 100UPZ (from the company Alpine). To complete, thepowder is sieved in order to obtain a size of the particles between 10and 110 μm.

The powders thus obtained respectively comprise a binder system composedof:

Example 4 Example 5 Example 1: 563 parts Example 2: 375 parts Example 3:187 parts Example 3: 375 parts

EXAMPLE 6 Characteristics of the Coating

The powders formulated as described in example 4 and 5 are applied withan electrostatic spray gun at a voltage of 60 kV on untreated coldrolled steel with a film thickness of 40 to 100 μm.

The coatings deposited are then subjected to melting in a mediuminfrared/convection oven (Triab) at a temperature of 140° C. during atime of approximately 3 minutes, and are then subjected to irradiationwith ultraviolet light emitted by a 160 W/cm Gallium-doped followed by a160 W/cm medium pressure mercury vapour UV-bulb (Fusion UV Systems Ltd.)with a total UV dose of 4000 mJ/cm².

The powder coatings obtained were tested; following results areperceived:

-   -   visual assessment: Example 4=good, Example 5=good.    -   For both powders a smooth and glossy appearance without any        defect was perceived.    -   MEK resistance: Example 4>200 double rubs, Example 5>200 double        rubs, which corresponds to the number of twofold rubbing        movements (to and fro) with a cotton pad impregnated with MEK        which does not detrimentally affect the appearance of the        surface of the cured film.    -   Reverse impact: Example 4=160 kg.cm, Example 5=60 kg.cm, the        value of resistance to reverse impact (RI) in kg.cm, according        to ASTM D2795 on cold rolled steel.    -   Direct impact: Example 4=160 kg.cm, Example 5=80 kg.cm, the        value of resistance to direct impact (DI) in kg.cm, according to        ASTM D2795 on cold rolled steel.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one of ordinaryskill in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

1. Radiation curable powder coating composition which comprises a) 10 to90% weight of a (meth)acryloyl group containing polyphenoxy resin havinga number averaged molecular weight ranging from 650 to 3500, b) 10 to90% weight of a (meth)acryloyl group containing resin, different fromthe (meth)acryloyl group containing polyphenoxy resin a) and from a(meth)acryloyl group containing amorphous polyester and wherein the(meth)acryloyl group containing resin b) is selected from (meth)acryloylgroup containing polyesteramides and/or polyurethanes and/or acryliccopolymers; and c) 0 to 30% weight of a (meth)acryloyl group containingmonomer or oligomer.
 2. Radiation curable powder composition accordingto claim 1 wherein the (meth)acryloyl group containing polyphenoxy resina) is the reaction product of (meth)acrylic acid with a glycidyl groupcontaining polyphenoxy resin.
 3. Radiation curable powder compositionaccording to claim 1 wherein the (meth)acryloyl group containingpolyphenoxy resin a) has at least one of following properties: a glasstransition temperature ranging from 30 to 80° C. a degree ofunsaturation ranging from 0.2 to 6.0 milliequivalents of double bondsper gram of (meth)acryloyl group containing polyphenoxy resin a meltviscosity (cone/plate at 200° C.) of less than 20,000 mPa.s. 4.Radiation curable powder composition according to claim 3 wherein thedegree of unsaturation ranges from 0.5 to 4.5 milliequivalents of doublebonds per gram of (meth)acryloyl group containing polyphenoxy resin. 5.Radiation curable powder composition according to claim 1 wherein the(meth)acryloyl group containing polyesteramide is obtained from thereaction of glycidyl(meth)acrylate with a carboxyl ic acid groupterminated polyesteramide.
 6. Radiation curable powder compositionaccording to claim 1 wherein the carboxylic acid group terminatedpolyesteramide used for the preparation of the (meth)acryloyl groupterminated polyesteramide is obtained from the reaction of a diaminewith a carboxylic acid group containing polyester, the polyester beingprepared from the reaction of one or more aliphatic, cycloaliphatic oraromatic polyacids with one or more aliphatic or cycloaliphatic polyols.7. Radiation curable powder composition according to claim 1 wherein the(meth)acryloyl group containing polyesteramide has at least one offollowing properties: a number averaged molecular weight ranging from800–16,000, degree of terminal unsaturation 0.15 to 2.00milliequivalents of double bonds per gram of polyester a glasstransition temperature ranging from 40 to 70° C. a melt viscosity(cone/plate at 200° C.) of less than 50,000 mPa.s.
 8. Radiation curablepowder composition according to claim 7 wherein the degree of terminalunsaturation is 0.35 to 1.50 milliequivalents of double bonds per gramof polyester.
 9. Radiation curable powder composition according to claim7 wherein the number averaged molecular weight ranges from 1,300 to8,500.
 10. Radiation curable powder composition according to claim 1wherein the (meth)acryloyl group containing polyurethane is obtainedfrom the reaction of an hydroxyalkyl(meth)acrylate and a poiyoi with apolyisocyanate.
 11. Radiation curable powder composition according toclaim 1 wherein the polyol used for the preparation of the(meth)acryloyl group containing polyurethane is a C2–C15 aliphatic orcycloaliphatic diol, a polyesterpolyol or a polyetherpolyol. 12.Radiation curable powder composition according to claim 1 wherein the(meth)acryloyl group containing polyurethane has at least one offollowing properties: a number averaged molecular weight ranging from800–15,000, degree of terminal unsaturation ranging from 0.15 to 2.00milliequivalents of double bonds per gram of polyester a glasstransition temperature ranging from 40 to 100° C. a melt viscosity(cone/plate at 200° C.) of less than 100,000 mPa.s.
 13. Radiationcurable powder composition according to claim 12 wherein the numberaveraged molecular weight ranges from 1,300 to 8,500.
 14. Radiationcurable powder composition according to claim 12 wherein the degree ofterminal unsaturation ranges from 0.35 to 1.50 milliequivalents ofdouble bonds per gram of polyester.
 15. Radiation curable powdercomposition according to claim 1 wherein the (meth)acryloyl groupcontaining acrylic copolymer is obtained from the reaction of: anacrylic copolymer having functional groups obtained from 40 to 95 molepercentage of at least one monomer having acrylic or methacrylic groups,0 to 60 mole percentage of another ethylenically unsaturated monomer and5 to 60 mole percentage of an ethylenically unsaturated monomer havingfunctional groups capable of reacting with an epoxy, carboxylic acid,hydroxyl isocyanate group, said monomer having a (meth)acryloyl groupand a functional group capable of reacting with a carboxylic acid,epoxy, isocyanate or hydroxyl group.
 16. Radiation curable powdercomposition according to claim 1 wherein the (meth)acryloyl groupcontaining acrylic copolymer has at least one of following properties: anumber averaged molecular weight ranging from 1,000 to 8,000, a glasstransition temperature ranging from 45 to 100° C. a degree ofunsaturation ranging from 0.35 to 3.50 milliequivalents of double bondsper gram of acrylic copolymer a melt viscosity (cone/plate at 200°C.) ofless than 50,000 mPa.s.
 17. Radiation curable powder compositionaccording to claim 16 wherein the degree of unsaturation is 0.5 to 2.5milliequivalents of double bonds per gram of polyester.
 18. Radiationcurable powder composition according to claim 16 wherein the numberaveraged molecular weight ranges from 2,000 to 6,000.
 19. Radiationcurable powder composition according to claim 1, which additionallycomprises up to 15 parts by weight of a photoinitiator for 100 parts byweight of the total of the (meth)acryloyl group containing polyphenoxyand the (meth)acryloyl group containing polyesteramide and/or the(meth)acryloyl group containing polyurethane and/or the (meth)acryloylgroup containing acrylic copolymer and/or the (meth)acryloyl groupcontaining monomer or oligomer, if present, and optionally aphoto-activator.
 20. Radiation curable powder composition according toclaim 19 wherein 0.5 to 8.0 parts by weight of photoinitiator for 100parts by weight of the total of the (meth)acryloyl group containingpolyphenoxy and the (meth)acryloyl group containing polyesteramideand/or the (meth)acryloyl group containing polyurethane and/or the(meth)acryloyl group containing acrylic copolymer and/or the(meth)acryloyl group containing monomer or oligomer, if present, andoptionally a photo-activator, is employed.
 21. Powder varnish or powderpaint comprising a radiation curable powder composition according toclaim
 1. 22. Process for coating an article wherein a radiation curablepowder composition according to claim 1 or a powder varnish or a powderpaint containing said composition is deposited on the article, followedby melting the coating thus obtained and by radiation curing the coatingin the molten state.
 23. Process according to claim 22 wherein themelting of the coating is achieved by heating the coating at atemperature of 80 to 150° C. and/or the curing of the coating in themolten state is achieved by exposing the said coating to UV radiation orto accelerated electron beams for a time which is sufficient to form acured coating.
 24. Process according to claim 23 wherein said time isfrom 0.5 to 10.0 minutes.
 25. Article partially or entirely coated bythe process of claim 22.